Purple question

Chris Dent adds purple numbers and paragraphs to Jason Kottke’s list of little things that are getting permanent addresses on the web. I think that’s right in some very interesting ways that are waiting for experiments and experience to show.
I have one big question about the usefulness of purple numbers that perhaps people who have worked with them can answer.
When I am editing, paragraphs are among the most malleable of units. Groups of a few sentences are combined to form larger paragraphs. Large paragraphs are split into smaller paragraphs. A few sentences from one paragraph are cut and moved to a different paragraph.
Therefore:
* purple references to an early draft will be very different from their referents in a later draft.
* the sequence will be garbled
* some references will be missing
So, perhaps purple numbers are only useful for final drafts — like a reviewed and published scientific paper.
But then, what about writing in wiki. When a wiki is used as a canonical writing tool, the content is malleable all the time. How confident can linkers be about the stability of a referent?
By contrast, a wiki page or a blog post is pretty stable. The content might change a lot (by the conventions and affordances of wiki) or a little (by the conventions and affordances of blog). But the topic is probably the same.
A del.icio.us link entry or a Flickr photograph is stable, although the description and tags may change.
In practice, are purple numbers stable enough to be useful? Or are there certain cases where they are more useful than others?